The invention relates generally to the field of power over local area networks, particularly Ethernet based networks, and more particularly to a method of communicating a settable priority from a powered device to associated power sourcing equipment.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to: reduced cost of installation; centralized power and power back-up; and centralized security and management.
The IEEE 802.3af-2003 standard, whose contents are incorporated herein by reference, is addressed to powering remote devices over an Ethernet based network. Power can be delivered to the powered device (PD) either directly from the switch/hub known as an endpoint power sourcing equipment (PSE) or alternatively via a midspan PSE. A PSE is defined as a device that provides power to a single link section.
The above mentioned standard prescribes a detection protocol to distinguish a compatible PD from non-compatible devices and precludes the application of power and possible damage to non-compatible devices. An optional classification protocol is prescribed, which enables classification of the power requirements of the PD to one of 5 classes. Of the 5 classes specified, 3 classes result in maximum power levels of the standard, namely 15.4 Watts at the output of the PSE. Thus, only 3 levels of power are supported by the classification protocol namely 4.0 Watts, 7.0 Watts and 15.4 Watts. Power is to be reserved by the PSE in accordance with the classification detected by the protocol.
The term PD is defined as a device that is either drawing power or requesting power from a PSE. Thus, a PD receives power, if available, from a PSE over the communication equipment. In a typical application, PD interface circuitry enabling the detection and optional classification is supplied. Power is isolated by the PD interface circuitry from the PD operational circuitry through an isolating switch, and is enabled to the PD operational circuitry only after the voltage at the PD, supplied from the PSE, rises to Von. One function of the PD interface circuitry is thus to close the isolating switch thus enabling operation of the PD operational circuitry. In a typical application, the output of the isolating switch is fed to the input of a DC/DC converter, and the output of the DC/DC converter powers the PD operational circuitry.
The standard further prescribes a maximum turn on time, designated tpon. In the event that the PSE powers the PD, power is to be supplied and a minimum current draw of 10 mA is to be monitored within tpon after completion of detection. After tpon a disconnect detection function is to be active in which the PSE is to monitor one or both of an AC maintain power signature and a DC maintain power signature.
No method of communicating information between the PD and the PSE is provided other than that provided by the detection and optional classification protocol. Thus, in the event that the PD power requirements are between the power levels supported by the classification protocol, power is to be reserved in excess of the actual power requirements. An increase in granularity would improve the overall power management of the PSE, and enable a larger number of PDs having power requirements less than the maximum power to be supported by a given PSE. Communication between the PD and the PSE would further enable the transfer of information such as PD temperature, priority of the PD, results of internal PD testing, PD configuration and PD type. Such information would advantageously enable improved power management and powering decisions.
U.S. Pat. No. 6,473,608 entitled “Structure Cabling System” issued Oct. 29, 2002 to Lehr et al. and U.S. Pat. No. 6,643,566 entitled “System for Power Delivery Over Data Communication Cabling Infrastructure” issued Nov. 4, 2003 to Lehr et al. the contents of both of which are incorporated herein by reference are addressed to the issue of supplying power to a PD over an Ethernet based network. No method of communication is described, and in particular no method of supplying increased classification granularity is described.
In a system operating according the IEEE 802.3af standard, preferably ports receiving power are assigned priority, as described in the above referenced U.S. Pat. No. 6,473,608. In the event of a shortage of power, preferably lower priority ports are disabled, or have power removed from them, prior to the disabling of higher priority ports. Priority is assigned to ports of the PSE, and in an exemplary embodiment priority is assigned by a configuration program in communication with the PSE.
Unfortunately, in actual practice, there is no certainty that the configuration program has been run. Additionally, any changes in wiring may not have been properly taken into account in assigning priority. Thus, there may be a situation where a port, which is to be assigned a high priority, receives a low priority assignment.
It would therefore be desirable to have a method of communicating priority from a PD to an associated PSE, while meeting the requirements of IEEE 802.3af. Thus, the installer of the PD, or alternatively an authorized user, would be empowered to assign a priority to the PD, which would follow the PD irrespective of connections.